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Questions About Humidity Indicator Cards and Baking Components?
Board Talk
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TranscriptPhil And welcome to Board Talk with Jim Hall and Phil Zarrow of ITM Consulting. The Assembly Brothers. Coming to you from ITM headquarters, high above Mount Rialto. We are here to talk to you about electronic assembly, materials, equipment, components, practices and procedures, among other things. Jim, what is the question du jour? Jim Okay. This is from M.B. We run small jobs so a reel of MSD components could be open and closed a number of times. Each time we put a new desiccant pack and a new humidity indicator card in the MSD bag and seal it. If we total all of the times we open the bag it exceeds 168 hours. Example, eight hours open then seal for one or more days, then we open the bag for ten hours and seal, etc. If the humidity indicator cards are not pink, do we still have to bake the components? Phil Interesting question. I will weigh in first by saying that humidity indicator cards are very helpful and useful. But in terms of finite accuracy, I think they are up there with the old temperature sensing labels. They get you in the ballpark. Would I want to hitch my wagon to that? Put it this way, do you feel lucky? The procedure calls for logging strictly in and when you exceed the exposure duration with the remaining components, you do the bake out. My answer to that is I wouldn't trust a humidity card, I would trust the time honored JEDEC 021 and 033. Jim I agree with you 100%. First off, for those of you not familiar, M.B. is talking about 168 hours. That is the floor exposure limit for a type 3 moisture sensitive device. The MSL of level 3 is 168 hours. It is probably the most common level that we deal with. The spec says that the total exposure is greater than that. The thing that I would point out is that the humidity indicator card is really only telling you about the integrity of the bag, the atmosphere in the bag. It is not really telling you what is going on in the heart of your little component. Think about it, your part is out for eight hours to use this example that M.B. provided. During those eight hours, the plastic package has absorbed moisture. That moisture is inside that package. So now you put it back in the bag and seal it up with desiccant. There is no moisture in the bag, and no moisture can get into it. But it doesn't really tell you what is going on with that moisture inside. I would point out that for all components if they are out for short exposure, this is clearly defined in J Standard 033, which you should have in your possession. Somebody in your organization should have that spec and be intimately familiar with it so that you can plan how best to deal with these things. It is not a big spec, it is only about 25 or 30 pages. A couple hours you can understand it pretty well. There is something in there called short-term exposure. I don't know the exact numbers, but the numbers 8 and 12 stick in my mind. So let's say it is 8. It says that if your part is not exposed for more than eight hours. If you put it back in the moisture sensitive bag, desiccant and seal it up, that part will reset to 0 in some long time interval. Which I think is the number ten. Don't hold me on these numbers, read the spec. Okay, you're out for 7 hours, that's less than eight. You close the bag up. If you keep that bag closed for 10 times 7, or 70 hours then the clock will be reset to 0. The idea being that this really dry air and desiccant does remove that little bit of moisture that you got into the bag. So that is for these multiple jobs. You may want to read that spec and see if you can take advantage of that if your storage in between runs is long enough. You may be resetting your clock to 0 on some of these things. But in all cases get that get that Standard 033. It is not big. Have somebody read it and really understand it. Then define a strategy that works for you in your environment with the frequency at which you open and close these bags. Phil My brother brings up a very good point. Jim I usually do. Phil Yeah, usually. Yes, you do. I won't make a trite comment. The point is, you really need to have somebody who understands the whole MSD story, as Jim was saying, in terms of 020 and 033 and understanding what it is all about. It is very important that your operators and tech understand it too so that they are diligent about replacing the bag and logging the time. We recommend, as Jim mentioned, somebody that is actually responsible. For lack of a better word, an MSD guru. Most facilities have somebody who is the go to person for ESD. You want to have it for MSD as well. You don't have to pay that person a lot of money extra, if anything. It would look good on their resume. We highly recommend that. Good. I think we covered that subject. Jim This is one of the most important topics that we see problems with when we audit facilities. We talk to our customers, we often see lack of clarity on their handling of their moisture sensitive parts. So M.B. the fact that you understand it to this level is laudable. Phil Well, very good. I just want to say though Tim Jensen wants to strangle us with the real preforms every time we say it, you have been listening to Board Talk with Jim Hall and Phil Zarrow. Whatever you do, whether you are dealing with expired MSD components or not, don't solder them like my brother. Jim And don't solder like my brother. |
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